Microwave-Assisted Solid-State Synthesis of Dichalcogenide Nanostructures for Electrocatalytic Hydrogen Evolution

We present a simple, fast, solvent-free, environmentally benign, one-pot technique to synthesize nanoflakes/nanoplatelets of transition metal dichalcogenides [i.e., molybdenum disulfide (MoS2), tungsten disulfide (WS2), and vanadium disulfide (VS2)]. In this technique, the precursor powder was prepared by simply mixing a transition metal source, a sulfur source, and multiwall carbon nanotubes (MWCNTs) in a mortar and pestle and heating in a microwave oven for 10 min under atmospheric conditions. MWCNTs were used as a microwave absorber. Microwaves interacted strongly with the precursor and induced localized arcing and plasma. Synthesized nanomaterials were studied using electron microscopy, X-ray and electron diffraction, Raman and photoelectron spectroscopy, and thermogravimetric analysis. The crystalline nanostructures were found to have mixed semiconducting and metallic phases. The as-synthesized MoS2, WS2, and VS2 showed impressive electrocatalytic activity for the hydrogen evolution reaction. MoS2 exhibited the lowest overpotential with a typical value of about 262 mV at a current density of 10 mA cm–2 and a Tafel slope of 84 mV dec–1, along with long-term stability. The proposed method is time- and energy-efficient and does not demand vacuum or a gaseous atmosphere, stringent temperature–pressure conditions, multiple steps or lengthy procedures, complex instrumentations, or expert manpower.